The interactions of an electromagnetic radiation with biological tissue at different frequencies are due to different mechanisms. At low frequencies the measured conductance and permittivity are due to ionic diffusion through the cellular membrane, at middle frequencies due to polarization effects of the macromolecular membranes and at high frequencies due mainly to the water content of organic macromolecules, their polarization and relaxation mechanisms.
The dielectric constant and the conductance of body tissues have been measured as a function of a wide range of frequencies by various authors. Most of the measurements have been of tissue samples, obtained from sacrificed animals or human cadavers.
Current measurements show a factor of up to 10 times higher permittivity of malignant tumors, as compared with that of adipose tissue and only slightly higher permittivity, when compared with permittivity of muscles and glands.
The measurement method of choice has been by measuring the reflection from the open ended waveguide when terminated by the tissue sample. See (Precision Open-Ended Coaxial Probes for In Vivo and Ex Vivo Dielectric spectroscopy of Biological Tissues at Microwave Frequencies; IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 53, NO. 5, May 2005). As obviously this method cannot be used for diagnosis from outside the body, several non-invasive methods have evolved.
The Dielectric constant of human tissue may also be imaged as a by-product of MRI imaging, utilizing the RF magnetic field induced by the RF coil, to reconstruct the dielectric constant and conductance distribution in real time, although this method may be an “overkill” from the cost point of view. (see http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4113345/).
In principle the RF magnetic field (B.sub.1) induced by the RF coil, which detects the Larmor frequency oscillates at the of the target nuclei, reorients the net nuclear magnetization of the spins so that a MR signal can be induced and detected by the receive coil. Both the excitation of the nuclear magnetization and the reception of signal intensity rely on interactions between applied RF magnetic fields and local electrical properties, namely the real dielectric constant .epsilon..sub.r and the conductivity .sigma.. Knowing the magnetic B.sub.1 transmit and receive fields provide the necessary information for extracting the local permittivity .epsilon..sub.r and conductivity .sigma.. see (magnetic resonance based electrical properties Tomography—http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4113345/#!po=69.53-13)
There are numerous research papers attempting to map the permittivity of body tissues by irradiating the area with microwave beams and reconstructing its permittivity from the distribution of the scattered radiation detected from the outside the area. The different implementations of the method attempt to solve the electromagnetic inverse scattering problem, which in principle is ill-posed. If an “a priori” assumption of a solution is assumed, the real solution may be arrived at by successive approximations, using for example the Newton-Raphson method. “Regularization” techniques attempting to resolve the ill-posed problem of scattering, may enable to reconstruct simple phantoms, such as a small high dielectric constant sphere depicting a tumor, within a large low dielectric constant sphere, depicting the breast. However in practical applications, where there are high permittivity contrasts between adjacent tissues, the high permittivity contrasts between adjacent tissues, trump the possibility to arrive to a unique solution and result in “smeared” reconstructed images.
Measuring the scattered radiation from a tumor in order to find its location and permittivity is strewn with measurement problems that result in very low signal-to-noise ratios. The path of an electromagnetic wave to a presumed tumor and back is twice the distance to its one-way position and in all cases leads to a very low signal-to-noise ratio. as evidenced by the poor images obtained.
Breast cancer is the most common malignant disease in women worldwide. According to the International Agency for Research on Cancer (IARC) in 2012. there were 14.1 million new breast cancer cases diagnosed and 8.2 million cancer related deaths, worldwide. The estimates show that in 2012 there were 32.6 million people alive, over the age of 15, that were diagnosed in the past with breast cancer. X-Ray mammography still remains the “GOLD standard” for diagnosing breast cancer, despite its many limitations such as 10-20% false negatives. in the USA in the 12 months, thru Sep. 1, 2015, 39,052,521 mammography procedures were reported by 14,963 full Field Digital Mammography units; namely an average of 2681 procedures/year.
Most countries recommend screening mammography every year after age 40 and every 2 years from age 50 and on (to age 69 in Europe) and to age 74 (in US). The different recommendations are a compromise between the proven benefits of early detection and the potential damage of X-ray radiation. In addition to the potential X-Ray damage, women also feel uncomfortable with breast compression that although improves diagnosis, may be painful and discourages attending the annual checkup. False positives lead to unnecessary biopsies as roughly 10% of mammograms show images with possible tumors, but less than 10% of those are diagnosed as malignancies. Most importantly, mammography misses up to 15% of actual tumors, some of which were even detectable by palpation.
All of these limitations and their associated potential for additional health risks provide ample incentive for the development of alternative modes for breast imaging.
Ultrasound may be used to complement mammography and identify the nature of large masses but cannot be used as the sole modality for breast cancer imaging.
Melanoma is the least common of skin growths, but the most deadly one. It is estimated that in the USA there will be around 75,000 new cases of invasive melanoma and around 10,000 deaths, in 2015.
The incidence rate of melanoma has doubled since 1973. Currently there is no foolproof, non-invasive test for detecting melanoma, but having a skin biopsy.
In summary, there is great importance in developing a non-ionizing diagnostic method that can differentiate between Benign and Malignant growths including small growths in the margins and reduce if not eliminate biopsies.